Let's preface this by saying that I think fighting outside of a sanctioned event is stupid and you are a moron and a public nuisance if you engage in it. That being said, sometimes it is unavoidable because even though I think 85% of all people in the world are decent and sensible people, the other 15% ruin a lot of things in life for the rest of us.
I have unfortunately been involved in a number of bar fights, although I never initiated them. Recently, there was an unruly guy who was horrendously drunk and being a nuisance in a local sports bar that I frequently go to. Although I was not directly involved, both of the guys who were, were starting to make a scene and it was clear that neither one of them really have any idea how to fight. I wouldn't have gotten involved but one of them made a wild swing at the other one and accidentally struck one of the bar staff who is a tiny and very sweet young woman. That's when I got involved and it was over very quickly.
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Anyone who has any experience in fight training will likely tell you the same thing in that fighting in public is exceptionally stupid because even as a trained fighter who knows how to use their fists will agree that the opportunity for you to injure yourself simply by hitting someone else is very high. Skulls are hard and fingers have a lot of bones in them that can get hurt. You may not care about the damage that you do to the other person but a broken finger takes a very long time to get over and there isn't really anything that can be done to speed up the recovery process. Of all of the trained fighters that I have met over the years there are very few of them that have been involved in fights in public. Perhaps this is because we have discipline and don't actually want to hurt people or perhaps it is because we know that we are a lot more capable of casing real damage than the average Johnny Drunko in a bar.
When I was training in a Krav Maga school, the trainer informed all of us that if we were EVER involved in a public fight that we started, that we would immediately be kicked out of the program. This was a bold statement on his part because this fledgling school was barely paying the bills but he was extremely serious about it and when exactly this sort of situation happened to one of the students he stuck by his word and kicked him out of the school. Trained fighters don't actually want to fight and will do almost anything they can to avoid it. So should you, whether you are trained or not, should the situation arise.
In my situation, I wasn't even involved in the disagreement and I don't really even know what it was about. I just happened to be in the vicinity and when the woman who was also not involved got hit, it was now my time to get involved to break things up.
A fantastic way to immobilize an opponent in any situation while making it almost impossible for the person to cause you any harm while also doing minimal harm to them is a rear choke. This can be done from the front as well but you leave yourself open to damage should the person decide to bitch out and punch you in the groin. For the most part though, when a person has their air supply and blood flow to the brain suddenly cut off, they become compliant pretty rapidly.
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One you get this locked in, and it should be relatively easy, make sure to put your head as close to theirs as possible, with your head tilted to the side so if they try to rear head-butt you, it wont cause any damage. This position also makes it very difficult for them to strike you in the head and even if they can, they won't be able to cause much damage with it. Again, the grip you have around their neck is going to prevent them from being able to do very much in this regard anyway because most people, and especially untrained people are going to be trying to remove your arm from their neck and this is very difficult to accomplish, even for a trained fighter.
Of course it helps if you are not significantly smaller than the person who you are attempting to subdue, but even if you are, there isn't really a whole lot the person can do if you have this locked in properly, like the picture above shows. If you have the foresight and ability to do so, you can make this maneuver even more effective by taking them down to the ground with you underneath them. I suppose this part of the process could be a little bit dangerous for you but this is why you do this in a rolling fashion to protect you from accidentally body-slamming yourself. The main focus here is to not lose your grip on their neck but if you have your arm locked in properly, there is very little chance of them getting out unless they are covered in Vaseline.
In my situation, I was talking to the guy while it was going on and telling him "just give up and come outside with me and I will let you go." It took about 8 seconds for him to agree but had he waited another 5 seconds or so he would have been unconscious anyway. The only bad thing that happened during all of this was that the other person involved in the fight threw a few punches at his head while I had him locked up even though I was shouting at him to stop it. His friends subdued him but not before he accidentally punched me in the hand as well, jamming my finger.
Thankfully, the guy who I had locked in kept his part of his word and did end up walking outside with me where we had a chat about how he needs to pay his bar tab if he has one and he needs to go. He made no attempt to hit me at this point but I had my hands up in the ready position should he decide to go all ape on me.
The staff of the bar did the right thing by also telling the other guy that he had to leave as well, even though he was a regular there. Both of these guys are permanently banned from the premises as they should be.
The moral of the story here is two things: The main one is to not get into fights in public or really at all if you can help it. Fighting is stupid and even when you win you lose. Think about it for a second? Are you really going to feel good about yourself because you hurt another person? If you do then you are a psychopath and need to perhaps join an actual gym to get some of that rage out of your system on a heavy bag rather than on another person. Remember, there is always going to be someone tougher than you, no matter how hard you think you are.
The second lesson here is that a choke is probably the best thing that a person can possibly have in their fighting arsenal. I've studied kickboxing, Krav Maga, Muay Thai, Wing Chun, and wrestling. The rear naked choke is the most effective way of ending any violent encounter and this is the reason why so many MMA events end with precisely that sort of thing.